Off-stoichiometric Na(3−3x)V(2+x)(PO(4))(3)/C nanocomposites as cathode materials for high-performance sodium-ion batteries prepared by high-energy ball milling

Na(3)V(2)(PO(4))(3) (NVP) is regarded as a promising cathode material for sustainable energy storage applications. Here we present an efficient method to synthesize off-stoichiometric Na(3−3x)V(2+x)(PO(4))(3)/C (x = 0–0.10) nanocomposites with excellent high-rate and long-life performance for sodium-ion batteries by high-energy ball milling. It is found that Na(3−3x)V(2+x)(PO(4))(3)/C nanocomposites with x = 0.05 (NVP-0.05) exhibit the most excellent performance. When cycled at a rate of 1C in the range of 2.3–3.9 V, the initial discharge capacity of NVP-0.05 is 112.4 mA h g(−1), which is about 96% of its theoretical value (117.6 mA h g(−1)). Even at 20C, it still delivers a discharge capacity of 92.3 mA h g(−1) (79% of the theoretical capacity). The specific capacity of NVP-0.05 is as high as 100.7 mA h g(−1) after 500 cycles at 5C, which maintains 95% of its initial value (106 mA h g(−1)). The significantly improved electrochemical performance of NVP-0.05 is attributed to the decrease of internal resistance and increase of the Na(+) ion diffusion coefficient.